Although the proliferation of digital signal processing equipment has met with widespread acceptance in a variety of industries, telephone companies have been slow to convert to or integrate digital signalling subsystems and communication schemes into their well established copper wire networks. One of the principal reasons for such reticence is the fact that a significant part, if not all, of an established telephone network employs analog signalling equipment. Consequently, to be accepted by the telephone company, any digital product must not only be a cost effective replacement for existing circuitry, but it must be signal-compatible with any remaining analog units of the network to which it may be interfaced.
Advantageously, the assignee of the present application currently offers to the industry digital signalling/interface units that enable digital services to be integrated into a variety of office environments, and allow digital signalling capability to be extended over a tandem communication link all the way to the customer site, without totally preempting the conventional use of analog signalling for maintenance and testing. Specifically, copending U.S. patent application Ser. No. 686,415, filed Apr. 16, 1991, entitled "Analog Service Channel Port for Digital Interface," by R. E. Bowlin et al, and co-pending U.S. patent application Ser. No. 752,777, filed Aug. 30, 1991, entitled "Digital Tandem Channel Unit Interface for Telecommunications Network," by C. L. Hall, each of which is assigned to the assignee of the present application and the disclosure of each of which is herein incorporated, describe respective types of digital data port or channel units that allow the replacement of conventional analog equipment with digital devices that are used for signalling, voice and data communications, while still retaining the ability to be interfaced with analog (tone) signalling equipment for carrying out maintenance and test procedures.
A requirement of this and any equipment installed in the communication network link is that it be maintained in good working order and, when necessary, be capable of being provisioned to meet changing user demands. Typically, status/performance evaluation and provisioning functions have been accomplished manually by a craftsperson on-site at the channel bank in which the equipment of interest is installed. In an effort to remedy the problem of rapidly escalating labor costs that now face the industry, a number of equipment suppliers have proposed replacing existing channel bank equipment with intelligent channel systems (smart channel banks combined with smart channel units).
One example of such a system is described in the U.S. Pat. No. 4,849,972 to Hackett et al entitled "Digital Data Communications Terminal and Modules Therefor." In accordance with this patented system, D4 channel bank equipment may be locally and remotely provisioned by way of an attendant microcontroller that is included as part of the common equipment. Each channel unit includes its own local microprocessor and associated NVRAM for storing provisioning data. All provisioning is effected by way of a supervisory communication path between the attendant controller and the channel bank. There is no capability of effecting remote provisioning through one or more tandem or cascade-connected channel units, through which multiple offices are interconnected with one another. In addition, the system of Hackett et al provides no mechanism for provisioning channel bank equipment from a test access location between two end offices, such as a test access location provided at a cross-connected interface within a site intermediate the end offices of the network. Consequently, as one would expect, a replacement solution of the type described in the Hackett et al patent has met with considerable resistance by the telephone companies due to the significant increase in per channel equipment cost, which is generally attributed to the need for a dedicated on site system controller (computer), enhanced channel bank common equipment, and the incorporation of resident intelligence into the channel units.